Improving or reducing viscosity of a coating material can improve the sprayability and the coating efficiency. Thinning with a solvent will improve viscosity but coating efficiency will be reduced and may require several coatings. The best method to improve viscosity while maintaining coating efficiency is by heating the coating material and is particularly effective in cold environments where low temperatures will increase viscosity. Further clean air regulations limit the amount and type of solvents that can be used with coatings. Therefore reducing viscosity with heat helps in complying with the clean air regulations.
One method of heating a coating material is to heat the supply reservoir. A disadvantage of this method is that when pumped long distances the coating material will cool. This could be overcome by heating the material an amount sufficient to compensate for cooling in a supply hose. A standard method for heating coating materials is to recirculate the fluid from a pump to a heater, then to a spray gun and back to the pump. This method is more costly initially, can require a bit of maintenance and is awkward to use by the sprayman.
Another known method is to heat the material from the supply as close to the spray tip as possible. One such method is disclosed is U.S. Pat. No. 4,036,020 issued Jul. 19, 1977. In this patent a fluid is heated as it flows through a nozzle passage by a heater comprised of concentric converging cones containing a hot fluid. The purpose of this patent is to expand and improve vaporization of a working fluid to produce a high velocity stream in a turbine.
In another invention disclosed in U.S. Pat. No. 3,632,042 windshield washer fluid is kept warm in a tube by hot coolant from the engine flowing in a coaxial tube. The engine coolant is used to heat the washer fluid throughout the path to the spray nozzles. The purpose of this invention is to prevent windshield washer fluid water from freezing in cold temperatures. This system simply prevents the washer fluid from icing and clogging the nozzle.
Another system for reducing the viscosity of a patent is described in British Pat. No. 700,595. In this invention a paint material is supplied to a spraying device after passing through a coil immersed in a hot water bath. A disadvantage of this system is that it is difficult to maintain an optimum temperature.
Other systems for preheating a fluid are disclosed is U.S. Pat. Nos. 930,346; 1,844,653 and 4,728,036. In these patents a fluid is preheated to improve atomization at a nozzle. The intent of these patents is to substantially increase vaporization to improve burning efficiency. These devices would not be advantageous for use with coating materials which flow best and coat efficiently at moderate regulated temperatures.
It is one object of the present invention to provide a system for reducing the viscosity of coating materials to keep the use of solvents in compliance with clean air regulations.
An additional object of the present invention is to provide a system for efficiently reducing viscosity of coating materials by controlled heating to improve spray quality.
Yet another object of the present invention is to provide a system for reducing or controlling viscosity that controls the maximum material temperatures while heating the heat sensitive materials. Temperature control prevents multiple component materials from reacting too quickly.
Yet another object of the present invention is to provide a system for improving viscosity that creates a "thin film" between a coaxial heating hose and an outer hose that increases the coating material surface in contact with the hose to improve temperature control and speed heating.
Yet another object of the present invention is to provide a system to improve viscosity by heating which includes an emulsion in the heating fluid that has a higher specific heat. The emulsifier increases the transfer of heat to the coaxial hose to the material being heated.
Still another object of the present invention is to provide a system for improving viscosity a coating material that includes a lubricant in the heating material to reduce line friction increasing flow substantially.
Still another object of the present invention is to provide a system for improving the viscosity of coating materials by heating that uses a dielectric medium circulated in the coaxial hose when used with electrostatic spray units and spraying electrically conductive coating to prevent shorting of the high voltage system.